For lead frames on which semiconductor elements are mounted, it is one of the important points for improving the reliability of products to improve adhesiveness of sealing resin to the terminal parts that are connected to semiconductor elements and to the outside. Accordingly, various technologies for improving adhesiveness of resin to prevent the terminal parts from coming out have been proposed. Specifically, these technologies include: a technology of forming a protrusion (eave-shaped portion) on the upper surface of terminal; and a technology of roughening the lateral surface of terminal.
For example, Japanese Patent Kokai No. 2011-151069 discloses a technology of making a lateral surface of a substrate rough by giving an etching treatment from the front and back surfaces of the substrate. This technology is a technology capable of coping with the above-described problem by making a difference between etching masks used for the front and back surfaces in a conventional etching process that has been performed in the prior art. In the technology disclosed in Japanese Patent Kokai No. 2011-151069, its objective is achieved by making a lead frame with etching masks that are formed in such a way that an etching mask used for the front surface is given narrow openings and an etching mask used for the back surface is given wide openings when the etching process is performed by the length substantially equal to or smaller than the thickness of the metal substrate.
Now, in the case where lead frames are made by the prior arts, a protrusion has to be formed in such a way that: the top end of the protrusion is substantially flat; or the cross section of the protrusion has an arc-like profile, because a crack occurs in a sealing resin in the case where the top end of the protrusion is sharp even though the protrusion is formed in order to improve adhesiveness of resin to terminal parts.
In the case of QFN (quad flat non-leaded package) or lead frames for LED in particular, an edge face of a device-mounting plane is designed to overhang an edge face of a plane that is exposed after semiconductor packaging, to function as one of measures for preventing resin from peeling off from a lead frame. However, the trouble which is acknowledged as problem in the present field is that resin inevitably peels off from a lead frame because of influences of: expansion or contraction of resin due to thermal history at high temperatures; and vibration, the expansion or contraction and vibration occurring due to friction between a lead frame sheet and a blade when the lead frame sheet is cut off into strips. Accordingly the marketplace in this field requires better improvement of adhesiveness of resin to lead frame.
Accordingly, the present invention is made in view of the above-described problem. The objective of the present invention is to offer a lead frame for mounting semiconductor element which effectively satisfies adhesiveness of sealing resin to lead frame.